(1) Field of the Invention
The present invention broadly relates to a liquid jet recording apparatus for recording data by means of a jet of a recording liquid (referred to also as "ink" hereinafter). More particularly, the invention relates to an ink tank for use in an ink jet recording apparatus and also to an ink jet recording head (referred to also as an "ink jet cartridge" hereinafter) having the ink tank integral therewith. Still more particularly, the present invention is concerned with an ink tank and an ink jet cartridge having improved means for detecting the quantity of ink remaining in the ink tank.
(2) Related Background Art
FIGS. 1 and 2 schematically illustrate two types of ink jet recording heads of the background art. Each of these liquid jet recording heads has an ink tank for storing a recording ink and a recording head tip (referred to also as an "ink jet unit" hereinafter) provided with an energy generating means for energizing the ink to be discharged from discharge ports in the tip so as to record data on a sheet of recording paper.
More specifically, referring to FIG. 1, an ink jet recording apparatus has a recording head tip, i.e., an ink jet unit, denoted by 1. The apparatus also has an ink tank 2 and a detector 3 for detecting the quantity of the ink remaining in the ink tank 2. The detector 3 has a pressure chamber 5 communicating with an ink supply passage 4, a diaphragm 6 for isolating the pressure chamber 5 from the atmosphere, and a switch 7 which is turned on and off in response to a deflection of the diaphragm 6. During the operation of the recording apparatus, the ink in the ink tank 2 is gradually consumed as a result of repeated jetting of the ink for the purpose of recording and also for the purpose of purging of any clogging port in the discharge port. In consequence, a negative pressure is generated in the pressure chamber 5 and the diaphragm 6 is deflected by the negative pressure so as to turn the switch 7 on, thereby emitting an electric signal 8 indicating that the ink tank 2 is becoming empty.
On the other hand, the liquid jet recording head shown in FIG. 2 has a flexible cable 9 connected to the recording head tip 1 and capable of supplying electrical signals thereto, and a pair of detection electrodes 10A and 10B disposed in the ink passage 4. In this case, the electrical resistance between these detection electrodes 10A and 10B is changed in accordance with a change in the quantity of the ink remaining in the ink tank, so that the quantity of the ink remaining in the ink tank is detected through detection of the resistance between the electrodes 10A and 10B.
The background art of FIG. 1, however, cannot precisely indicate the quantity of the ink remaining in the ink tank, because the change in the pressure within the pressure chamber 5 fluctuates due to fluctuation of precision of the parts which form the pressure chamber 5. In addition, the detector tends to erroneously produce an "empty" signal due to an impacting change in the pressure which takes place as a result of the purging. Furthermore, quite troublesome work is required for the installation of the detector, particularly when the ink tank is integrated with the liquid jet recording head tip.
The background art recording head of FIG. 2 also is disadvantageous in that the detection is often impeded due to presence of air bubbles in the ink. Namely, if air bubbles conveyed through the ink supply passage stagnate around the electrodes 10A and 10B, no electrical current flows between the electrodes so that the detector generate an "empty" signal even when a large quantity of ink remains in the ink tank.